Microwave hybrid joining of SAC305-Ni@Sn composite solder: Heating mechanism, mechanical reliability, and first-principles calculation

Microwave hybrid joining (MHJ) is an effective soldering technique characterized by high energy efficiency and uniform volumetric heating. In this study, Ni@Sn nanoparticles (NPs) were incorporated into a commercial Sn-3Ag-0.5Cu (SAC305) solder matrix. An in-situ observation method was employed to analyze the heat generation behavior under microwave irradiation. Reinforced (Cu, Ni)₆Sn₅ nano-IMC joints were fabricated using self-prepared SAC305–Ni@Sn composite solder paste under 2.45 GHz and 2 kW conditions. The MHJ joint achieved a shear strength of 44.28 MPa after only 60 s, reducing holding time by 42.9 % compared with reflow soldering while maintaining optimal mechanical properties. The addition of 1 wt% Ni@Sn NPs further increased the strength to 51.21 MPa, representing a 17.7 % improvement. After 1200 thermal cycles, the strength of the Cu/SAC/Cu joint fabricated by reflow decreased to 32.49 MPa, representing a 25.47 % reduction compared to the original joints. In contrast, the Cu/SAC-1 %Ni@Sn/Cu joints maintained a higher strength of 40.52 MPa, exhibiting only a 20.87 % decrease from the original strength, thereby demonstrating superior reliability under temperature cycling conditions. First-principles calculations further reveal that Ni doping improves the thermodynamic and mechanical stability of IMCs by suppressing electronic states near the Fermi level and enhancing orbital hybridization, thereby strengthening atomic bonding. This work proposes a novel and effective strategy for designing high-performance and thermally stable solder joints for advanced electronic applications.